Re: [patch v3] mm, page_alloc: reintroduce page allocation stall warning

[David Rientjes <rientjes@google.com>]

On Mon, 30 Mar 2026, Shakeel Butt wrote:

> > Previously, we had warnings when a single page allocation took longer
> > than reasonably expected.  This was introduced in commit 63f53dea0c98
> > ("mm: warn about allocations which stall for too long").
> > 
> > The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> > warn about allocations which stall for too long") because it was possible
> > to generate memory pressure that would effectively stall further progress
> > through printk execution.
> > 
> > Page allocation stalls in excess of 10 seconds are always useful to debug
> > because they can result in severe userspace unresponsiveness.  Adding
> > this artifact can be used to correlate with userspace going out to lunch
> > and to understand the state of memory at the time.
> > 
> > There should be a reasonable expectation that this warning will never
> > trigger given it is very passive, it will only be emitted when a page
> > allocation takes longer than 10 seconds.  If it does trigger, this
> > reveals an issue that should be fixed: a single page allocation should
> > never loop for more than 10 seconds without oom killing to make memory
> > available.
> > 
> > Unlike the original implementation, this implementation only reports
> > stalls once for the system every 10 seconds.  Otherwise, many concurrent
> > reclaimers could spam the kernel log unnecessarily.  Stalls are only
> > reported when calling into direct reclaim.
> > 
> > Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> > Signed-off-by: David Rientjes <rientjes@google.com>
> 
> Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
> 
> I am hoping that the reason you are reintroducing these warnings is
> because you already are seeing such cases in your production
> environment. Do you have anything interesting to share?
> 

We don't have this patch in our production environment (yet).  We've 
been stress testing allocations for page faults with lots of concurrent 
skb allocations that can keep us persistently below the per-zone min 
watermarks and hope that this patch will shed some light on some 
unresponsiveness issues that we've encountered if/when it happens.